1. Field of the Invention
The present invention relates to a device for an electrophotographic apparatus and, more particularly, to a device for improving the quality of ink supplied to the photoconductive drum in an electrophotographic apparatus.
2. Background Art
Supplying a consistently high quality of toner to a photoconductive drum is crucial for the proper operation of an electrophotographic apparatus during the printing process. An electrophotographic apparatus can be either one of a laser printer, an electronic copier, a facsimile machine, or any versatile office machine. The general operation of an electrophotographic apparatus starts with paper being loaded from a supply tray and then transported through to a high pressure transfer roller. The high pressure transfer roller transfers the toner image from the photoconductive drum onto the sheet of paper. Subsequently, the paper is transported to a fixing device that fuses the toner image onto the paper using both heat and pressure rollers.
To prepare the toner image for the high pressure transfer roller, it is necessary to attach toner particles to the latent electrostatic image on the photoconductive drum. The toner particles are applied by the developing unit and transform the latent electrostatic image into a latent toner image.
A toner cartridge charged with a static voltage is contained in the developing unit and supplies toner to the supply roller. The toner is stirred by an agitator that keeps the toner evenly charged and mixed. The electrostatically charged toner is transferred to the supply roller by the rotation of the agitator. The rotation of the supply roller then transfers the toner to a developing roller. The toner deposited on the developing roller is uniformly applied due to a doctor-blade that maintains a constant level of thickness of toner on the developing roller.
A photoconductive drum is charged by a charger roller with a static negative voltage. Then, the photoconductive drum is rotated and exposed to the light from a light emitting device. The parts of the photoconductive drum surface exposed to the light generate an latent electrostatic image. This latent electrostatic image is transformed into a latent toner image when toner particles are attached to the latent electrostatic image by the developing roller. A sheet of paper loaded from a paper tray is fed into the electrophotographic apparatus by a pickup roller. The paper is then transferred to a high pressure transfer roller that presses the paper against the photoconductive drum to transfer the toner image onto the sheet of paper from the drum. Then the paper, and applied toner image, is transported between the heating roller and the pressure roller of a fixing unit to fuse the toner image into the sheet using both heat and pressure.
More specifically, the developing roller is mounted between the photoconductive drum and the toner supply roller. Toner is stirred by the agitator and fed to the developing roller. A doctor-blade contacts the developing roller and controls the thickness of the toner applied to the developing roller. Then, the photoconductive drum rotates and brings the latent electrostatic image into contact with the layer of toner formed on the developing roller, thus developing a latent toner image. After developing the latent toner image, the toner that remains on the developing roller is partially recovered and mixed with the reservoir of ink supplied by the toner cartridge while most of the remaining toner stays attached to the surface of the developing roller. This re-using of toner can lower the quality of printed images.
Different innovations have been developed to regulate the toner used in an electrophotographic apparatus. By way of example, U.S. Pat. No. 5,317,370 to Kohyama entitled Developing Apparatus Including Means for Collecting Used Developing Agent, shows the removal of used toner from the toner supply roll. Both U.S. Pat. No. 4,989,037 to Nagatsuna entitled Device for Driving a Rotary Body and U.S. Pat. No. 3,918,808 to Narita entitled Photorecptor Cleaning Device for Electrophotographic Copying Apparatus of the Dry Cleaning Agent Type, mention devices for cleaning excess toner from a photoconductive drum.
I have observed that what is needed, but has so far been neglected in the art, is a developing unit that removes the toner remaining on the developing roller after the developing process is finished. This will avoid continuously stressing the re-used toner with pressures applied between the photoconductive drum and the developing roller and with the pressures applied between the developing roller and the doctor-blade. Thus, the degradation of printing quality, especially when a great number of sheets are being printed or after a long time has passed without operating the electrophotographic apparatus, can be eliminated. I believe that this inadvertent re-using of toner also causes the toner on the developing roller to have a non-uniform electrical charge. Consequently, images printed under some circumstances lack the high resolution otherwise possible. I expect that a developing roller that does not re-use toner that has been on the developing roller during a development process will improve the resolution of printed images and the usefulness of the associated electrophotographic apparatus.